Purpose/Significance of Application:Evaluation of the effectiveness and feasibility of in-situ biotransformation using molasses to treat groundwater contaminated with chlorinated solvents

Regulatory Requirements/Cleanup Goals:
Objective of study was to evaluate enhanced in situ biotransformation as a remedy for impacted groundwater. No cleanup goals were established.

Results:Data were provided for six downgradient monitoring wells (three in the upper and three in the lower water-bearing zone) for baseline samples that were collected in July 1999 prior to installing the treatment system, and again in September 2000. During this period, TCE concentrations appeared to have been reduced more in the upper water-bearing zone than in the lower water-bearing zone
- In the upper zone, TCE concentrations were reduced from 4,110 to 323 µg/L and from 3,310 to 345 µg/L in two out of the three downgradient monitoring wells. In the third monitoring well, TCE concentrations stayed approximately the same at 378 µg/L
- In the lower zone, TCE concentrations were reduced from 2,770 to 2,300 µg/L in one out of the three downgradient monitoring wells. In the other two wells, TCE concentrations increased from 1,020 to 2,150 µg/L and from 3,170 to 4,450 µg/L

Cost Factors:- The total cost for the pilot study was $306,557, including $152,903 in capital costs, $72,560 in O&M costs, and $27,094 in other project costs such as reporting and project management
- Unit cost was not calculated for this application
- No information was provided about the projected cost for use of this technology at full-scale at this site

Description:The NWIRP in Dallas, TX is an active plant that manufactures and assembles military and commercial aircraft components and weapons systems. Improper disposal of degreasers in these operations resulted in contamination of the groundwater with TCE and its daughter products. In October 1999, a field demonstration of enhanced in situ biotransformation was initiated in an area near Solid Waste Management Unit (SWMU) #15, which was an unlined acid neutralization pit that received liquid wastes from site operations between 1970 and 1983.

The demonstration consisted of injecting molasses solution into the upper and lower water-bearing zones using two injection wells, to serve as a supplemental energy source for indigenous microbes and enhance the existing microbial processes occurring within the subsurface. After an 11 month period, sampling showed that TCE concentrations appeared to have been reduced more in the upper water-bearing zone than in the lower water-bearing zone. In the upper zone, TCE concentrations were reduced by more than 85% in two out of the three downgradient monitoring wells, while they stayed approximately the same in the third well. In the lower zone, TCE concentrations were reduced by approximately 15% in one out of the three downgradient wells, and increased in the other two wells. No information was provided about the projected cost for use of this technology at full-scale at this site. During the demonstration, mold was found to be growing on the molasses solution. As a result, the solution was prepared in batches and automated injection was switched to manual events followed by thorough cleaning of the molasses mixing tanks.